TLDR: SQL-92, also known as the SQL-2 standard, was introduced in 1992 by the ISO (ISO SQL Standard) and ANSI (ANSI SQL Standard) to establish a comprehensive framework for database query language consistency and interoperability. It built upon the earlier SQL-89 standard, introducing new features like joins, subqueries, and support for null values, making it a pivotal advancement in SQL's evolution.
https://en.wikipedia.org/wiki/SQL-92
One of the key features of SQL-92 was its formal support for inner joins, outer joins, and cross joins, enabling more robust and flexible query capabilities. These constructs allowed developers to combine and manipulate data across multiple tables with greater precision. Additionally, the introduction of subqueries enhanced query nesting, allowing complex logic to be expressed in a concise and readable manner.
https://www.w3schools.com/sql/sql_join.asp
SQL-92 also improved data integrity through the introduction of constraints such as `CHECK`, `FOREIGN KEY`, and `DEFAULT`. These additions ensured that data met specific criteria before being entered into a table, aligning with database normalization practices. Furthermore, the standard provided support for `NULL` handling, clarifying its behavior in comparisons and aggregate functions, which significantly reduced ambiguity.
https://dev.mysql.com/doc/refman/8.0/en/create-table-foreign-keys.html
Despite being succeeded by later standards like SQL-99, SQL-92 remains a foundational reference for modern database systems. Its legacy is evident in its widespread adoption, as many contemporary relational database management systems (RDBMS) like PostgreSQL, MySQL, and Oracle Database continue to support SQL-92 syntax and features, ensuring backward compatibility.